I found one yesterday entitled, How to Make a Goldfish Live for Decades. It gives you a whole bunch of tips on how to supposedly increase the longevity of a goldfish. Well, let me tell you the real secret of long lived goldfish: strawberry milk.
Yes, you heard me right. When I was about ten and my sister was five, we got a goldfish. It was our first pet, and since we were allergic to anything with fur, it was our only pet. My sister christened it Johanna after her best friend, even though to this day I'm pretty sure it was a dude.
A few weeks after Johanna's arrival my sister was leaning over the tank admiring the fish. Unfortunately, she had a cup of strawberry milk in her hand (a completely disgusting drink that she was unaccountably fond of). She leaned too far, and into the water went the strawberry milk. And I don't mean a few ounces. The entire cup went into the drink (pun intended). Scared of the consequences, she ran and hid in her bedroom, telling nobody about the incident. It wasn't until that night when my mother went to feed the fish, and noticed that despite the filter the water was looking weirdly pink and cloudy that we found out what happened. Sis tearfully admitted that she had spilled her strawberry milk into the tank. She seemed much more upset that she had lost a perfectly good cup of strawberry milk than concerned for the fish. My mom filled a bowl with water and put Johanna in it temporarily and set about changing the tank, but she was far from hopeful. After all, Johanna had been stewing in a suspension of tank water and milk for eight and a half hours. And the filter had stopped working (apparently strawberry milk is too much for a ten gallon filter). So when her environment was clear of contaminants, we returned Johanna to her tank and waited for her/him (the world's first transexual goldfish) to suddenly start floating belly up.
She/he never did. In fact, that fish died only three years ago. By the time she/he died, it was about nine inches long. My mother, who hadn't realized when she bought us a goldfish that she was investing in a life partner, continually threatened to have the thing filleted. To this day, we all swear that it was the strawberry milk that kept Johanna alive so long.
Note: While this story is true, I can't really prove that strawberry milk is good for fish, so don't try it. If you must, it was strawberry Nesquik, which I'm not sure they even make anymore.